Growing concerns regarding domestic security have created a critical need to positively identify individuals as legitimate holders of credit cards, driver's licenses, passports and other forms of identification such as those for the military or drivers of hazardous materials, or school teachers, etc. The ideal identification process is reliable, fast, and relatively inexpensive.
A well-established method for identification is to compare a fingerprint with a previously obtained authentic fingerprint of the individual. Fingerprints have traditionally been collected by rolling an inked finger on a white paper. Attempts to employ an electronically imaged fingerprint method use, as a key component, a solid-state device such as a capacitive or optical sensor to capture the fingerprint image in a digital format.
A typical fingerprint comprises a pattern of ridges separated by valleys, and a series of pores that are located along the ridges. The ridges are usually 100 to 300 μm wide and can extend in a swirl-like pattern for several mm to one or more cm. These ridges are separated by valleys with a typical ridge-valley period of approximately 250-500 μm. Pores, roughly circular in cross section, range in diameter from about 60 μm to 240 μm and are aligned along the ridges and can be isolated or grouped into two or more abutting or near abutting features. There are typically more than 400 pores within a fingerprint region with a frequency of occurrence of about 21 pores/cm of ridge length. Almost all present-day fingerprint identification procedures use only ridge/valley minutiae patterns. These are simplified and identified as a pattern of ridge/valley features such as end points, deltoids, bifurcations, crossover points, and islands, all together referred to as minutiae. Typically, a relatively large area of the fingerprint is required in order to obtain enough unique minutiae features, for example, at least 0.50×0.50 inches. Most modern fingerprint imagers therefore use up to one full inch square or even larger, in order to obtain enough features to perform a useful means of identification. Fingerprints are compared using primarily this simplified description of the minutiae patterns.
Due to the more demanding resolution requirements necessary to successfully image friction ridge detail and/or pores, and the requirements for enrolling and analyzing such high resolution imagines, there are no commercial devices available today that use friction ridge detail and pores for fingerprint identification, even though there are typically 7 to 10 ten times as many pores as minutiae in a given fingerprint area. A typical fingerprint image as small as 0.1×0.1 inches may only contain 2-5 minutiae points, not enough to reliably identify a unique individual. The same area, however, may typically contain as many as 40 to 50 pores and several thousand ridge contour details, which along with a few minutiae points can positively identify an individual reliably.